Injector-burner for metal melting furnaces

ABSTRACT

The following invention relates to an injector-burner for applications in the metalwork field, in particular for use in electric arc furnace melting processes having a frontal head with two series of holes arranged in two concentric crowns, the inner crown of holes used to feed fuel and the outer crown used to supply a supporter of combustion. A central hole is also provided, which is fitted with an oxygen injection nozzle. The holes of the two crowns are divided into groups separated by circular sectors without holes, in order to create a number of flames and are inclined in such a way as to give the gases supplied, and consequentially the flame generated, a rotation around the injector-burner axis. By regulating the flow-rates of the fuel and the supporter of combustion supplied to the various holes, the injector-burner is able to regulate the flame shape in burner mode and also in injection mode, thus guaranteeing optimum performance in all modes.

This application claims priority to PCT/EP2003/007431 entitled InjectorFor Metal Melting Furnaces, filed on 9 Jul. 2003, which claims priorityto Italian Patent Application No. MI2002A001526, filed on 11 Jul. 2002.

TECHNICAL FIELD

The following invention relates to a multipurpose oxygen injector withbuilt-in burner (hereinafter referred to as injector-burner) for use inthe metallurgy either for the heating and metallurgical processing ofmetals or as an aid to other metal heating and metallurgical processingappliances used in melting. The injector-burner may additionally thoughnot exclusively be used in electric arc furnaces (or EAF).

The device can be fixedly wall-mounted above the level of the liquidmetal bath. In certain applications, it can also be moved towards theinterior of the furnace in order to reduce the distance from the bath.

A method for use of this device for melting processes in electric arcfurnaces is also disclosed.

BACKGROUND ART

Many systems for oxygen injection from furnace walls are known. A numberof such systems make use of an additional flame to regulate the initialheating and melting of the metal charge, which is usually activated bynatural gas as the fuel and oxygen as the supporter of combustion.

The drawback of the models currently available is that the devicesdescribed do not allow varying the shape of the flame at will in thevarious melting procedure phases.

At the start of the melting process, a diffuse and wide flame is notablyneeded in order to uniformly distribute a large chemical powerthroughout the solid charge. Subsequently, a concentrated flame mode isrequired, which is adapted to transfer heat to the residual solid chargebelow the injector installation level.

No state of the art injection device is known which is adapted toregulate the shape of the flame between these two opposite typologies.In particular, electric arc furnaces, hereinafter referred to as EAF, inwhich the state of the art injectors are used, suffer from bad heatdistribution. The type of burners (and injectors in burner mode)typically used in EAF produce a concentrated flame that producessomewhat inefficient blending and oxidises the charge in the initialphases of the melting process.

When used in burner mode, the known injectors present large fractions offree oxygen in the flame, a characteristic that, combined with thestrongly localised heating effect of the flame on the charge, makes themmachines suitable for oxygen lance cutting the metal charge, but not forheating it uniformly. The oxidation of the charge in the initial phasesof the melting process causes serious losses to the global energybalance as well as a drop in the final metallic yield.

Further drawbacks of this type of device are caused by the concentrationof the flame produced. The volume of the heated metal charge remainslimited, whereas the perforation of the charge as far as the electricarc area is a frequently observed phenomenon, which results in thedisturbance of the arc and causes the burnt gases to rise up along theelectrode without passing through the charge, to which heat is nottransferred efficiently. Moreover, the ring of metal charge at the baseof the column present in the furnace is preheated in a discontinuousway, with the consequence that the furnace must contain a greater numberof injectors.

In addition to these limits in burner mode, the injectors currentlyavailable are also not efficient in the injection of supersonic oxygen,carbon and lime.

The installation of such injectors on the walls of EAF requires that thejets produced by the injector are coherent, at least with regards to thedistance between injector and liquid bath. This characteristic is notsatisfied by the state of the art devices when the installation distancefrom the bath is greater than 750 mm. As a consequence, the oxygen,carbon and lime injections into the liquid bath and the slag areinefficient, with a consequential lengthening of refining times and thethermal overload of the internal volume of the furnace and the fumesystem caused by the reagents dispersed above the bath.

No state of the art injectors are known which are adapted to injectingfuel such as methane into the slag and/or molten bath in order to give acarburation reaction of the bath and simultaneously develop heat andreduce the oxides in the slag.

Patent documents GB-A-2064094 discloses a burner having holes throughwhich fluent fuel can be discharged within an outwardly divergentenvelope and further passages encircling the first passage through whichan atomising fluid can be discharged into the fuel as it leaves theburner head. U.S. Pat. No. 6,289,677 discloses a fuel injector for a gasturbine engine with a nozzle tip including an annular array of airpassages spaced radially from a central fuel injector passage. The axesof the passages are arranged so as to permit mixing of air and fuel. Asecond annular array of air passages is provided to produce a circularshape of the flame.

The shape of the flame produced by such burners of the known art iscircular and not suitable for hitting a surface from above whereby partof the energy is dissipated above the surface. Furthermore it cannoteject gas at supersonic velocity.

SUMMARY OF THE INVENTION

A new type of injector burner has been developed, in particular for usein the metallurgy field, more precisely, for melting furnaces such aselectric arc furnaces. The primary aim of the present invention is tosolve the above mentioned drawbacks of the state of the art, by creatinga multi-purpose injector-burner capable of satisfying the requirementsof each phase of the process and improving the energy balance,productivity and performance of the furnace in which it is used.

The injector-burner according to the invention comprises a cylindricalbody defining a first longitudinal axis, the cylindrical body comprisinga first central duct arranged along said axis, at least one second,ring-shaped duct, arranged around said central duct, a third ring-shapedduct, arranged around said second duct, a head, fixed to one end of saidbody and provided with at least one first through hole, coaxial to thefirst longitudinal axis and connecting said first central duct with theoutside of the injector-burner, the head being provided with second andthird through holes connecting respectively said second and thirdring-shaped ducts with the outside of the injector-burner, each secondthrough holes defining second respective axes, each second respectiveaxis forming a first angle with a plane passing through the first axisand the intersection point of the respective axis with the externalsurface of the head and furthermore each second respective axis defininga projection on said plane, forming a second angle with said first axis,wherein the second and third holes are divided into several groups, thegroups being reciprocally separated by circular sectors of the externalsurface of the head without holes, whereby the circular sectors havetheir apex on the first axis and their angles are greater than theangular distance between two adjacent second holes.

The first hole is coaxial with the cylindrical body. A third ring-shapedduct is arranged around said second duct and the head is provided withthird holes connecting said third duct with the outside. Said thirdholes each have their own axis forming a first angle with a planepassing through said first axis and the point of intersection of thehole's axis with the external surface of the head (intended as thecontinuation of said surface not considering the presence of the firsthole) and having a projection on said plane forming a second angle withsaid first axis of the cylindrical body.

Said first angles and said second angles of the second and third holescan advantageously be between 5 and 60°, the first and second angles ofthe second holes may also be different from those of the third holes.The latter is preferably such that the axes of the second and thirdholes, in pairs, cross over one another outside the burner. For makingsome particular embodiments like those for a flat, or fan-shaped, flamethe second angles can also be of value zero for some holes. Being theholes adapted to emit jets of gases supplied to the injector-burner'sducts, this device allows a good blending of the gases originating fromthe second and third holes, which should preferably be arranged oncircular crowns concentric with the first axis of the cylindrical body.They are divided into more groups spaced out by circular sectors of thehead without holes. Said sectors are defined between two sides of anangle having the vertex at the centre of the head (intersection betweenthe axis of the cylindrical body and the outer surface of the head),which is greater than the angle with its apex at the centre of the head,and having as sides the straight lines passing through said centre andthe centres of the two adjacent second or third holes, if present. Twoor more of such groups may be present.

Advantageously, the orientation of the axes of the burner second andthird holes with respect to the axis of the burner itself is chosen inorder to generate divergent flames and flame envelopes of variousshapes. The shape can be chosen in view of an optimal heat distributionin the scrap layer during the whole stage of scrap melting.

A particularly advantageous flame shape is the one with a flat and wideflame envelope. This solution offers an optimal use of the heatproduced, whereby the cavity produced by the flame of the burner lastsfor a longer part of the scrap melting phase, before an aperture isproduced in the part just above the flame. Avoiding such an apertureabove the flame is an important advantage, as through this aperture partof the heat flows directly in the upper furnace atmosphere withoutthermal exchange with the scrap.

Such a shape of the flame is produced by an appropriate selection of theangles of inclination of the axes of each hole or group of holes made onthe burner head. In this case two first groups of holes, set on the headsymmetrically and opposite to each other with respect to the head axis,have hole axes skewed in such way that first angles have valuescomprised between 5° and 60° and second angles have a value ofsubstantially 0°, i.e. the hole axes are coplanar with the head axis andsubstantially intersect the burner axis. Additionally two second groupsof holes have respective axes skewed in such a way that first and secondangles have values different from 0° and are thus not coplanar with theburner axis. The two symmetrical flames ejected by the second group ofholes interact with each other and with the flames ejected by the firstgroups of holes and produce altogether a flame envelope corresponding toa unique, wide and approximately flat flame.

The first duct, or the corresponding first hole, can have a convergingor converging-diverging nozzle shaped part, for regulating the expansionof the gas flowing in the duct, from the supply pressure to the outputpressure. Inside the first duct, a further fourth duct may be presentand preferably, coaxial with it, in order to supply solid or liquidcomponents, preferably dispersed in a gas, for example the powdersrequired by the process which are transported by a gas such as air oroxygen.

The invention also relates to a method for introducing gas into a metalmelting furnace, in particular electric arc furnaces, including theintroduction of gases to an injector-burner as described above.

The invention also relates to a method for heating and/or treating metalmaterial in a melting furnace, in particular electric arc furnaces,comprising the supply of a gas containing oxygen to the first duct of aninjector-burner as described above, a gas containing a fuel to thesecond duct, e.g. methane or natural gas, and a gas containing oxygen tothe third duct, where present.

The invention also relates to a further method of processing the metalin a melting furnace providing the injection of a fuel such as methanein the molten bath also through the first duct of the injector-burner.

Thanks to the characteristics concerning the conformation of the holeson the head, the injector-burner may produce a flame of varying shapesaccording to the requirements of the various phases of the meltingprocess when used in burner mode.

It is also able to function in oxygen injection mode (even in supersonicregime) and in the various production forms, it can also operate theinjection of solid powdered or granule material, such as carbon or lime.

The device solves the state of the art typical drawbacks, as it can workin burner mode during the melting phase, creating a diffuse flame in theprocess' initial phase and a concentrated flame in the concluding phaseof melting and subsequently working in supersonic oxygen or carbon orlime injector mode in the liquid bath refining phase.

The changeover between these injection and combustion different phasesand modes takes place by simply regulating the flow-rates in the variousinjector nozzles.

Another advantage obtained is the ease with which the injector-burner ofthis invention can replace the state of the art injectors or burners incommon melting furnace installations, thus obtaining considerable costsavings.

The injector is composed of a cylindrical body manufactured from verysimply constructed concentric tubes connected to a cylindrical head, forexample in copper. This injector is therefore compatible with existinginstallations, and can replace injectors of the known type withoutrequiring alterations to the housings of such machines on the furnacewalls.

Alternative set-ups that do not divert from the spirit of this inventionare also obviously possible.

In the fixed installation mode, the injector-burner can be wall-mountedin the same way as the state of the art, or on the platform of the EBT(eccentric bottom tapping), i.e. the typical eccentric area of modernmelting furnaces from which the tapping of the molten mass takes placeat the end of the process.

Installation in this area of the melting furnace makes it possible toexert the heating and treating action of the liquid mass in an area ofthe furnace that is usually cool, which is critical to the speed ofmelting operations.

It can also be advantageous that the injector-burner is mobile inrelation to the furnace, in order to be moved towards the interiorduring the melting and refining of the molten mass inside the furnace.

BRIEF DESCRIPTION OF DRAWINGS

Further characteristics and advantages of the finding will be furtherevident in view of the detailed description of a preferred, though notexclusive, embodiment of a burner for an electric arc melting furnacesuch as illustrated by way of non limiting example with the aid of theappended drawings wherein:

FIG. 1 illustrates a front view of the type of injector-burner accordingto the invention;

FIGS. 2, 3, 4 and 5 illustrate longitudinal section views of theinjector-burners according to various aspects of the present invention;

FIG. 6 illustrates various layout diagrams of the second and third holesof the head of an injector-burner according to the invention, togetherwith the section normal to the axis of the injector-burner of the flamegenerated by them;

FIG. 7 illustrates the pattern of the gas flow rates supplied to theinjector-burner described herein in the various phases of an iron scrapmelting process in an electric arc furnace;

FIG. 8 illustrates the curve with the trend followed by the percentageof reacted fuel as a function of the distance from the head of aninjector-burner conforming to this invention used in burner mode, incomparison with a state of the art device;

FIG. 9 illustrates a three-dimensional drawing of the evolution of theflame produced by the injector-burner in its operating mode generating awide flame;

FIG. 10 presents a three-dimensional drawing of the evolution of theflame produced by the injector-burner in its operating mode which formsa concentrated flame;

FIG. 11 shows a schematic view of a track of a flat wide flame producedby a further embodiment of the burner according to the invention;

FIG. 12 shows a schematic perspective view of several tracks of theflame of FIG. 11 during its propagation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference in particular to FIG. 1, the front view of aninjector-burner for the production of heat and for metallurgic treatmentin an electric arc furnace is shown, which comprises a head 2,manufactured from suitable material, usually copper and a cylindricalbody 3. The head 2 has a plurality of holes arranged alongcircumferences or circumferential arches concentric to the axis of thehead and the burner. The cylindrical body 3 of the burner 1, defines anaxis 6 and is constituted by more coaxial tubes inside one another. Thedirections 4 and 4′ of the axes of holes 5 and 5′ of the second andthird holes respectively are shown. Each axis of holes 5 and 5′ isskewed with respect to the axis 6, so as to define two angles:

-   i) angle α, different from zero, defined as the angle between the    projection of the axis of hole on a radial plane, passing through    the axis 6 and through the centre of the hole, and the axis 6 of the    body 3;-   ii) angle β, defined as the angle at which the axis of the hole    crosses a radial plane passing through the axis 6 and through the    centre of the hole.

As shown in FIG. 1, the axes intersect each other preferably in groupsof two, they open outwards and they have a tangential component inrelation to the axis of the injector-burner. By supplying fuel to thesecond holes and a supported of combustion to the third holes (or viceversa) flames will be obtained which rotate around axis 6 of thecylindrical body 3, producing a swirling effect. The first hole 7 isalso visible.

FIG. 2 illustrates a longitudinal section of an injector-burnermanufactured according to a possible embodiment of the invention. Itshows the first duct 8, the second duct 10 and the third duct 9, andalso a jacket 11, which is optionally provided, destined to thecirculation of a cooling fluid, for example water, defined from variouscoaxial tubes, collectively indicated with reference 12. Ducts 13 and13′ are used for the supply and removal of said fluid. The gases aresupplied to the ducts through pipes, such as those indicated with 14.The first hole 7 is coaxial with the cylindrical body 3. The drawingalso shows the converging-diverging portion 15 at the end of the firstduct 8, particularly suitable in the case of supersonic gas outflow inthe first duct 8. The converging-diverging, portion is preferably shapedin such a way as to convert the supply pressure into the dischargepressure following a hyperbolic tangent trend along the portion.

Either oxygen or a gas containing oxygen may be supplied in the firstduct.

In the embodiment shown in the drawings, the head 2 presents tworing-shaped chambers 19 and 19′ that serve for the distribution of thegas of the second duct and the gas of the third duct, these gasesgenerally being a supporter of combustion and a fuel, e.g. oxygen andmethane respectively (although it is also possible to change the orderof the supplies, if necessary) to the second and third holes 5 and 5′that lead from them. Other embodiments are nevertheless possible, forexample with more chambers destined for the distribution of the fuel andsupporter of combustion connected to the exterior through a number ofconcentric hole distributions made in head 2.

FIG. 3 illustrates a longitudinal section of a burner-injectormanufactured according to an alternative embodiment of the invention. Inthis case, the converging-diverging portion is replaced by a simpleconverging portion 15′. The diameter of the first hole 7 and the firstduct 8 are chosen to suit the characteristics of portions 15 or 15′.

FIGS. 4 and 5 refer to a longitudinal section of embodiments featuringthe converging-diverging portion and fourth duct 16, separated from thefirst duct 8 by tube 17, said fourth duct being used for theintroduction of powders or granules (such as carbon or lime)transported, for example, by a suitable gas flow, and with the firstduct straight without converging or converging-diverging portions, whichcan be used to inject powders together with the gas of the first duct.In this last case, the first hole may contain a consumable tube (20 inFIG. 5), made of steel or other suitable material, aimed at protectingthe walls of the first duct of the device from the abrasive action ofthe powders or granules; according to an aspect of the invention, theintroduction of the solids takes place in a gas flow, whose outflow fromthe injector-burner head is subsonic.

Other combinations are possible, according to process and plantrequirements.

As mentioned previously, the second and third holes (if present) shouldpreferably be distributed on two concentric circular crowns, as shown inFIG. 1. They can be divided into a number of groups spaced out bycircular sectors of the head without holes. Said sectors are definedbetween two sides of an angle having the apex at the centre of the head(intersection between axis of the cylindrical body and the outer surfaceof the head) greater than the angle with the apex at the centre of thehead and sides the straight lines passing through said centre and thecentres of the two adjacent second or third holes (if present). Two ormore groups may be present in order to form two or more flames whichwind around the axis of the injector-burner, thus giving good heatblending and distribution. The direction of the second and third holesis such as to give the gas jets a direction component tangential to theaxis of the injector-burner. In FIGS. 6 a-6 e different possible holelayouts are illustrated, which will give different types of flame in theinjector-burner operating mode that provides injection of fuel and asupporter of combustion through such holes, and which can be chosen asrequired. With suitable hole layout and direction, flames of the desiredshape will be obtained, shapes that can be adjusted to suit processrequirements. Beside each type of head, the section of the flamegenerated is shown, normal to the axis of the injector-burner at acertain distance from it, a flame that is generated, in particular, byoperating in “diffuse flame” mode as described below.

FIG. 6 b illustrates a particularly preferred aspect of the invention.

The second and third holes can also be shaped to form converging orconverging-diverging nozzles in order to give a supersonic outflow ofthe gases supplied therein.

A further preferred embodiment of a burner according to the presentinvention, particularly suitable for generating wide and flat flames. Inthis embodiment, the holes 4′, 4″ are grouped on the burner head in oneor more first groups 5 of holes, with interspaces of angle γ, greaterthan the angle δ, separating two adjacent holes. Preferably two of thesefirst groups 5 of holes are set on the head symmetrically and oppositeto each other with respect to the head axis 6. The angles α′, α″ ofthese holes 4′, 4″ have values comprised between 5° and 60° and theangles β′, β″ of the holes 4′, 4″ have a value of substantially 0°, i.e.the hole axes are coplanar with the head axis 6. Moreover, the holesaxes substantially intersect the burner axis 6. The angles α′, α″ andβ′, β″ are the same as previously defined in the other embodimentsdescribed above.

In this manner the two opposite first groups of holes 4′, 4″ aresuitable to produce two flames symmetrical with respect to the axis 6and divergent from the head tip so that the two flame axes intersect theaxis 6 of the burner behind the head. For example each hole 4′, 4″ ofthe first group is symmetrical with respect to the axis 6 to anotherhole 4′, 4″ of the second and opposite group of holes.

In this embodiment the head 2 is provided also with one or more secondgroups of holes 5, whose holes 4′, 4″ are oriented like in the otherembodiments previously described, i.e. both angles α′, α″, β′, β″ ofthese hole axes are different from 0° and thus are not coplanar with theaxis 6 of the head 2. The two symmetrical flames interact with eachother and with the other flames generated by the other groups of holesand produce a flame envelope corresponding to a unique, wide andapproximately flat flame, as shown in the FIGS. 11, 12: FIG. 11 showsschematically a cross section of a flat flame obtained with the presentembodiment, FIG. 12 shows several cross sections of a propagating flatflame

In all the embodiments foreseen in this invention, the injector-burnercan either be fixedly mounted on a wall or on a mechanical hand thatallows it to be moved inside the melting furnace.

In the fixed wall-mounted installation, the axis of the injector-burnercan be directed at will on both horizontal and vertical planes.

The injector-burner can be mounted on any state of the art wall or doorlance (moved by mechanical hand). Its design and the performance of itsjets are superior to the state of the art (particularly with regards tothe supersonic oxygen thanks to the special nozzle design) and allowinnovative use of such lances in relation to the state of the art.

It is to be noted that the state of the art lances of the knowntechnique are forced to operate at typical distances of 300-350 mm fromthe bath due to the scarce coherence of the jet of oxygen they produce.Only by operating at such close distances the efficiency of oxygenpenetration into the bath is acceptable.

In any case, the state of the art lances suffer from very limitedreliability and duration due to the fact that operating so close to themolten bath, they are in critical thermal and physical conditions andcan be directly affected by molten metal splashing.

If mounted at the end of a mobile lance, this injector-burner canprovide high injection efficiency even if its point of insertion isfurther from the bath than the applicative state of the technique. It ispossible to obtain injection efficiencies equal to or greater than theexisting lances by operating at a distance of up to 1-1.5 metres. Atthese distances, the duration of the lance is far superior, as it makesit possible to operate further from the bath and is therefore lessstressed by thermal and mechanical factors and is not at risk frommolten metal splashing.

This peculiarity also makes it possible for the injector-burner to beapplied in an intermediate installation mode between the fixedwall-mounted installation and the installation on a lance with amechanical hand fitted with numerous degrees of freedom of movement,both modes being typical to the state of the art.

A compact mechanical hand with only one axial degree of freedom can bewall-mounted, which allows for the introduction of the injector-burnerinto the furnace according to its axial direction. In thisconfiguration, the vertical and horizontal angles of installation of theinjector-burner are not altered, and the distance between theinjector-burner and the bath alone is varied.

This degree of axial freedom always permits maximum injectionperformance, irrespective of the current position of the liquid level,which depends on the quantity of metal charge in the furnace, theprocess phase and the state of wear of the refractory vat.

In any case, the minimum operating distance from the bath can, even inthis case, be higher than that of a state of the art standard lance andtherefore the problems of thermal—mechanical wear on the injector-burnerare reduced. Typically, a distance of 500-600 mm from the bath can bechosen.

The axial stroke of wall-mounted introduction device (typically 1-1.5meters) and, as a consequence, the external dimensions of the machinecan therefore be reduced, when the injector-burner is brought into linewith the wall during the loading phase.

We will now describe some operating modes of an injector-burneraccording to this invention, characterised in that it has second andthird holes, distributed on concentric circular crowns.

In the “diffuse flame burner mode”, the supporter of combustion issupplied from the third holes, or outer crown of holes and the fuel fromthe second holes or inner crown. The first central hole is fluxed with aminimum air flow-rate, in order to keep it clean. In this mode, theshape of the flame produced by the injector-burner is regulated by thephysical effect of the swirl, caused by the inclination of the secondand third holes that tends to cause a widening of the flame, whichcombines with the effect produced by the degree of separation of thefluxes produced by each set of holes, whose intensity depends on theangle of spacing between them.

Arranging the second and third holes in separate and spaced out groupsproduces an effect whereby the flame widens with continuity and does notclose in on itself as the ring-shaped flame produced by a head withoutspacing between the groups of holes would.

FIG. 6 b refers to a section of the diffuse flame produced by thepreferred embodiment of this invention. The resulting flow presents fourflame areas. A slight swirl effect is obtained that gives the jets aspatial helical configuration. The resulting flow presents 4 partiallyinteracting flame areas, given that the swirl effect associated to thereduced separation between the sets of holes causes a recirculation ofthe combustion products towards the injector-burner axis area. In thisway, 5 main fire directions can be identified. The opening of the fourouter flames is lower than the geometric direction of the holes. In thespace left free between the groups of holes, the environmental gas isable to flow, attracted by the action of the flows produced by theindividual groups of holes, thus supplying the axial region of theinjector-burner. The flows produced by each group can therefore expandspatially following the direction imposed by the inclination of theholes. The fluidodynamic connection between the surrounding environmentand the axial area of the injector-burner in fact prevents theproduction of a central depression area, which would cause the flame tocollapse.

The flame rotates in space, as it is moved further from the head, with aconsiderable increase in its efficiency.

FIG. 9 illustrates the evolution of the flame produced by the preferredmodel of this invention in the diffuse flame mode, with sections 21, 22,23 and 24 of it at 0.5, 1, 1.5 and 2 meters from the head 2 of theinjector.

In general, the swirl effect, coupled with the fact that the supporterof combustion and fuel jets are directed in such a way as to collide inpairs, causes an excellent blend of the reagents for which theinjector-burner in burner mode develops almost all of its power onsmaller distances from the head than the state of the art burners (orinjectors in burner mode).

FIG. 8 shows a graph that permits a comparison between the percentage offuel that has reacted with the supporter of combustion according to thedistance of the head along the axis for an injector-burner according tothe invention, represented by the H curve, and for a state of the artburner (or injector in burner mode) for application in EAF, representedby the L curve.

As one can observe from the graph, the injector-burner of this inventionused in the burner mode exhausts the combustion reaction at 200-300 mmfrom the head, whereas a conventional burner (or injector-burner inburner mode) requires more than 700 mm to obtain the same exhaustion ofthe combustion reaction.

This flame behaviour, combined with its particular shape assumed inspace, is at the origin of a series of advantages over the state of theart injector-burners in particular technical applications such as metalmelting in EAF.

In particular, in addition to radiance, the heating effect of the metalcharge takes place, through the convection of combustion products, whichhave an oxidising power on the charge, which is many times lower thatthe oxygen. The minimization of the flame region with non-reactedsupporter of combustion implies the minimisation of the oxidising effectwith regards to the charge.

Therefore, minimum oxidation of the charge is obtained, thanks tooptimised blending, the absence of oxygen-rich areas and the lowvelocity of the flame produced. The melting of the metal charge is givenby the heat produced by the flame and not by the oxygen lance cutting,in the presence of uniform heating and avoiding the oxidation of themetal charge, with gains in the global energy balance of the furnace'smelting process.

The volume of the heated charge is 3÷4 times greater that theconcentrated flame burners (and injectors in burner mode) of the knowntype.

With the embodiments provided by the present invention, the flameproduced has a frontal section many times higher than the state of theart injectors (ten or more times).

Flame injection is softer and better distributed, thus preventing theperforation of the charge until the electric arc area, avoidingdisturbance to the arc and preventing the combusted gases from rising upalong the electrode, without passing through the metal charge.

It is possible to pre-heat the entire charge ring at the base of thecolumn in the furnace without leaving areas of discontinuity with areduced number of units installed.

The hot gases produced by combustion move up inside the charge moreslowly and in a more uniform way and therefore have more time totransfer their energy to the metal charge.

Typically, the maximum power of a state of the art burner (or injectorin burner mode) beyond which its usage in EAF becomes inefficient andcauses the problems mentioned above, is around 2÷3 MW.

The design of the injector of the present invention is such to produce avery diffuse flame obtained as the sum of a number of individualpartially interacting flames with different directions in space.Typically, 4-5 main flame directions can be recognised. In this way,each injector can introduce into the furnace a power 2÷4 times higherthan the injectors of the known kind without risking the concentrationof energy in punctual areas only and thus maintaining a continuouspre-heat on the entire circumference of the furnace. In burner mode, theinjector described herein can reach 8÷10 MW and beyond, withoutencountering the disadvantages that characterise devices of the knowntype. It is therefore possible to introduce more power into the furnacewithout increasing the number of units installed and therefore thecomplexity of the machine.

In conformity with the invention, it is possible to create burners thatgenerate a flame as the sum of a number of flows/flames with apredefined degree of independence between them, characterised by thegeometrical separation of the sets of holes. The shape of the flame inspace is regulated by the development and opening of the swirl effect ofthe holes and by the spacing between groups.

One significant embodiment of the invention is that in which the secondand third holes are arranged in a regular way along the circumferenceand are not grouped together. If they are distributed in a uniform andcontinuous way around the axis of the injector-burner and are broughttogether, at equal inclination of the supporter of combustion and fuelholes, the presence of the swirl effect alone will produce a reducedwidening of the flame. In fact, in this case, the flame widens at theoutlet of the head according to the vector induced by the swirl, butclose to the head, it tends to close in on itself. This occurs because,at a certain distance from the head, the momentum of the jets isdissipated and is not able to maintain the depression in the axial areawith the consequence that the flame closes in on itself, thus becomingconcentrated once again. This embodiment therefore produces aconcentrated flame, but offers the advantage of improved reagentblending at outflow from the head compared to injectors of the knowntype.

In the “concentrated flame burner mode”, the supporter of combustion issupplied from the first central hole and the fuel from the inner crownof third holes. The outer crown of second holes is fluxed with a minimumflow-rate of air in order to keep it clean. In this way, the naturalwidening of the flow produced by the spatial direction of the crown offuel holes is inhibited by the momentum of the central jet, whichattracts the entire flow-rate of fuel injected around itself. A stronglydirectional flame guided by the axial jet of the supporter of combustionis therefore produced.

FIG. 10 shows to two axial sections 25 and 25′, which are between themorthogonal, the direction of the flame produced by the injectordescribed herein in the concentrated flame mode.

The flow of supporter of combustion is attracted by the axial jet, butpreserves its helical direction induced by the spatial orientation ofthe holes. This spiral development of fuel flow wrapped around the axialjet of the supporter of combustion increases the efficiency of theinjector in concentrated flame burner mode.

The changeover from “diffuse flame burner mode” to “concentrated flameburner mode” takes place during the process when the melting of themetal charge reaches the point in which the level of the charge dropsbelow the level of installation of the injector-burner.

With the “concentrated flame burner mode” it is possible to obtain astrongly directional, high density and power concentration flame thatmakes it possible to melt the residual solid charge and start to oxidisethe charge present at the level of the liquid bath. Changeover to thismode is made necessary by the charge in shape of the charge inside thefurnace, for which in this phase, the diffuse flame would cause a strongdispersion of heat directly towards the walls of the furnace and thefume system. The concentrated flame on the other hand, permits thetransfer of all the heat developed by combustion to the residual chargeto be melted and to the bath.

Changeover from the “diffuse flame burner mode” to the “concentratedflame burner mode” can also take place gradually, using the “hybridburner mode”. In the hybrid mode, the supporter of combustion issupplied both by the central nozzle and the outer crown of holes,whereas the fuel is supplied by the inner crown of holes. In this mode,it is possible to obtain all the intermediate flame shapes between the“diffuse” and the “concentrated” flame simply by varying the ratio ofthe supporter of combustion flow-rate injected by the central nozzle andthe flow-rate of the supporter of combustion injected by the outer crownof holes.

Flame regulation can therefore take place gradually.

In the “supersonic oxygen injection mode”, the oxygen is suppliedthrough the central nozzle, whereas the crowns of holes are fed with theminimum air flow-rate. Once the charge has completely melted and hasbeen completely transformed into the liquid state, the bath must berefined by injecting high velocity oxygen at a great depth.

This function is performed by the injector-burner, which is fitted witha nozzle on its axis that permits the injection of the chosen flow-rateof oxygen (from 600 to 10000 Nm³/h according to the size of the meltingfurnace and the specific process requirements) with a velocitycorresponding to Mach 2 or higher.

In this mode, the jet of oxygen presents higher characteristics than theknown type, especially if the shaped converging-diverging portion isincluded in the first duct.

The design of said nozzle is such to guarantee an injection efficiencyhigher than that of the state of the art even with considerableinstallation distances from the bath (greater than 1.5 meters).

The central converging-diverging nozzle is preferably configured with anaerodynamic profile in order to convert the total supply pressure(typically higher than 10 bar) into velocity, thus adapting to dischargepressure, following a hyperbolic tangent law such as:f(x)=a·th(c−b·x)+din which:

$\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}{{a = \frac{p_{0} - p_{s}}{2}};} \\{{b = \forall};}\end{matrix} \\{{d = \frac{p_{0} + p_{s}}{2}};}\end{matrix} \\{{c = {{ath}\left( \frac{1 - d}{a} \right)}};}\end{matrix} \\{{{{th}(\kappa)} = \frac{{\mathbb{e}}^{\kappa} - {\mathbb{e}}^{- \kappa}}{{\mathbb{e}}^{\kappa} + {\mathbb{e}}^{- \kappa}}};}\end{matrix} \\{{{ath}(\gamma)} = {{{th}^{- 1}(\gamma)}.}}\end{matrix}$when p_(o) is supply pressure, p_(s) is discharge pressure, x is thelength travelled by the gas in the nozzle portion, b represents anarbitrary factor that determines the degree of draft of the profilearound the throat section and can take any value (usually between 1 and3) and f(x) is a function to which the pressure in the various sectionsof the nozzle remains proportionate.

This type of profile guarantees perfect oxygen expansion inside thenozzle until it reaches the outlet condition. On the outlet section allthe thermodynamic quantities and the velocity profile are extremelyuniform thus guaranteeing maximum supersonic jet performance in terms ofjet coherence. As a consequence, the jet of supersonic oxygen canpenetrate deep down into the liquid bath, even if the injector isinstalled on the furnace wall at a distance of more than 1,5 meters fromthe bath. The coherent region (in which the velocity of the gases alongthe axis of the jet, coinciding with that of the injector-burner, doesnot diminish, i.e. it remains equal at least for 99% to that of the gason the surface of the injector-burner head) of the jet produced by thistype of converging-diverging nozzle is typically 2-3 times longer thanthe state of the art injectors. The injector of this invention canproduce perfectly coherent jets of oxygen up to distances of 2÷2.5meters.

This peculiarity allows efficient oxygen injection deep into the bath,which leads to an acceleration of the refining process. Moreover, thanksto its coherency, the momentum transmitted to the liquid bath reaches amaximum as does the stirring and the mixing of the liquid bath.

When the injector is orientated in such a way as to produce a jet thatis not orthogonal to the bath (on the vertical plane) and/or notdirected towards the axis of the furnace (on the horizontal plane), astrong bath stirring effect on the vertical and/or horizontal plane iscaused. This effect gives the liquid a great chemical and thermaluniformity, with obvious advantages with regards to both product qualityand refining speed.

During the injection of supersonic oxygen from the central nozzle, thetwo crowns of second and third holes are fed with a minimum quantity ofair in order to keep the holes clean. This air flow wraps itself aroundthe jet of oxygen in a spiral way, being attracted to it by the Venturieffect, exactly the same way as happens in the concentrated flame burnermode. The presence of this spiral flow of air around the jet of oxygendoes not damage the coherency of the jet, in fact it slightly improvesit, given that the shear rate drops in relation to the environment andtherefore the dissipation of kinetic energy of the jet due to viscousfriction.

It is also possible to adopt a “hybrid supersonic oxygen injection mode”in which, in addition to the injection of supersonic oxygen from thecentral nozzle, the burner function is kept on the crowns of holes oronly methane is injected by the inner crown of holes. The flame producedby fuel and supporter of combustion (injected by the inner crown ofholes and the outer crown of holes in the first case and by the innercrown of holes and central nozzle in the second respectively), isattracted by Venturi effect to the supersonic oxygen jet and it wraps itself around it in a spiral. The presence of this helical flame aroundthe oxygen jet further increases jet coherency, given that in additionto reducing viscous dissipation, it produces a high temperature fluidbuffer around the jet. Thanks to their high temperature, the burnt gaseshave a low density and can therefore easily be dragged by the oxygen jetwithout significantly reducing kinetic energy.

The presence of this spiral flame that wraps itself around the oxygenjet makes it possible to reach coherent jet lengths higher than theapplications of the known technique in which oxygen jets are protectedby a purely axial ring-shaped flame devoid of circumferentialcomponents.

When the flow-rate of a fuel such as methane, injected around supersonicoxygen, is such that combustion does not exhaust itself along the freejet, a quantity of non-reacted fuel reaches the slag and the moltenbath. In such conditions, air or oxygen can be injected by the outercrown of holes in order to perform a post-combustion reaction that willnow be described in detail. The oxidising effect induced by thesupersonic oxygen in the area of impact on the bath causes high localtemperatures of the molten metal (>1800° C.). At such temperatures thefuel that arrives on the bath gives the cracking reaction (for exampleif the fuel is methane):CH₄+energy→C+2H₂and it therefore divides into carbon and hydrogen. The reaction isendothermic and therefore cooling takes place in the area to avoidexcessively high molten metal temperatures (and therefore metalevaporation with a consequential drop in furnace performance) andfavours slag foaming. The carbon carburises the liquid bath, whilst thehydrogen reduces the oxides present above the level of the bath and inthe slag. This reduction reaction also interests the metal oxide presentat the level of the bath and permits an increase in the yield of themelting process, by recovering metal that would otherwise be lost in theslag. The part of the hydrogen that is unable to find oxides to reduceburns with the part of the oxygen injected that does not penetrate intothe bath or with air (or oxygen) injected together with the jet from theinjector's outer crown of holes. This post-combustion hydrogen reaction:2H₂+O₂→2H₂O+Energyreleases energy and a large quantity of gas (water vapour) that rise upthrough the slag causing it to foam. The same oxide reduction reaction,in part carried out by the hydrogen causes the production of a largequantity of water vapour. Slag foaming is very efficient and joinstogether with that caused by the rise of the CO produced by thedecarburation of the bath. Overall, one observes a rapid reswelling ofthe slag that has beneficial effects on the thermal balance of theprocess and on the efficiency of the electric arc.

Hydrogen post-combustion may also take place above the slag should theair or oxygen flow produced by the injector's outer crown of holes bereduced in such a way as to not penetrate into the slag.

The operating mode described above can be described as “hybrid oxygeninjection—carburation—reduction and post-combustion mode”. This phase isapplied in flat bath conditions.

The same injector-burner can also be used extremely effectively in the“pure carburation mode”. This takes place when the fuel is injectedthrough the converging-diverging central nozzle. In this case, if theflow-rate of the fuel is sufficiently high (depending on the size of thenozzle and typically higher than 100 Nm3/h) the fuel jet is verycompact, has high momentum and can even reach the supersonic regime. Thepenetration of the fuel in the bath is therefore very efficient. In thiscase too one has the fuel cracking reaction in carbon and hydrogen. Thecarbon carburises deep within the bath, whilst the hydrogen reduces theoxides present at liquid bath level and in the slag and subsequentlyreturns up through the slag where or above which it can givepost-combustion with an air flow (or oxygen) wrapped around the axialfuel jet and produced by one or both of the injector's crowns of holes.This phase is also applied in flat bath conditions. The regime of gasinjection containing fuel can be sub- or supersonic according torequirements and the conformation of the first duct.

The embodiments of the present invention previously described andillustrated in FIGS. 2, 3, 4 and 5 have “diffuse flame burner”,“concentrated flame burner”, “hybrid burner”, “Hybrid oxygeninjection—carburetion—reduction and post-combustion” and “purecarburetion” modes as described above.

More particularly, the embodiments illustrated in FIGS. 4 and 5 allowthe injection of solid material in powders or granules (such as carbonand lime), having a nozzle on the axis dedicated to the injection ofsuch materials during the refining phase. In particular, the embodimentillustrated in FIG. 4 permits the simultaneous injection of gas (such asoxygen) in a supersonic regime and material in powder or granules (suchas carbon or lime) as it bears a converging-diverging nozzle on its axisfor oxygen, with an insert inside the tube for solid material injection.

In any case, the central nozzle may also be used for injecting a gascontaining oxygen in order to operate. the post-combustion of the carbonmonoxide released from the liquid bath during the refining phase.

Generally speaking, for all the embodiments of the injector-burnerprovided by this invention and for all the operating modes, there is nolimit to the stoichiometric relations between the fuel and the supporterof combustion that can be used.

The invention also concerns a heating, melting and metallurgic treatmentprocess of metallic material in a melting furnace, in particularelectric arc furnaces, including the supply, to the first duct of aninjector-burner as described above of an oxygen-containing gas, to thesecond duct of a gas containing a fuel, such as methane or natural gas,and a gas containing oxygen to the third duct, if provided. Thisinvention also contemplates methods for introducing gas in a meltingfurnace with gas supply in different ways, as will be described below,for both the heating of the metallic material and its decarburation orcarburation.

As demonstrated, the device resolves the typical problems of the stateof the art, having the possibility to work in burner mode during themelting phase, by creating a very diffuse flame in the initial phase ofthe process and a concentrated flame in the conclusive phase of melting,and subsequently to work in supersonic oxygen or carbon or limeinjection mode during the refining of the liquid bath.

The changeover between these various phases and injection and combustionmodes takes place by simply regulating the capacities of the injector'svarious nozzles.

As an example, we will now give a possible programme of iron scrapmelting process in an Electric Arc Furnace, using an injector-burnerwith a third duct as described above, according to the presentinvention.

FIG. 7 illustrates the profiles of the fuel and supporter of combustionflow-rates in the various phases of the operation. The profiles serve asexamples only and have a relative value. In general it is not possibleto give absolute flow-rate and time values as they depend on the size ofthe furnace, the power of the arc installed and the number of chargingsto be made (single or multiple buckets). However, the usage logic of theinjector-burner remains unchanged.

Step 1: Powering Up

The burner is powered up a few tens of seconds later than the electricarc in order to ensure that the conditions of inflammability of themixture of fuel and supporter of combustion have been reached. The fuelflow-rate in the second duct is initially set at 30-50% of the nominalpower and a slightly reducing combustion ratio is maintained, withoxygen supplied in the third duct (in the case of O₂/CH₄ ratios ofapproximately 1.6:1.8 are adopted, i.e. 20-40% less than thestoichiometric ratio).

This is to obtain a flame that is suitable for heating but that isnon-aggressive towards the equipment in order to avoid damage to thecooled, non-cooled and refractory panels and the device itself. Afterworking in this way for approximately 30″, the burner's gas flow ratesand therefore its power can be increased to 80% of the nominal value andan almost stoichiometric ratio is used (in the case of O₂/CH₄ ratios ofapproximately 1.9-2.0 are adopted). During this time, the central ductfitted with a converging-diverging nozzle is fed with compressed air oroxygen. The flow-rate is thus calibrated so that the outlet velocity ofthe gas is at. least 80-120 m/s and pressure is 0.4-0.8 bar. In thecase, for example, of a nominal 300 Nm₃/h nozzle, 300-350 Nm₃/h can beintroduced. The primary aim of such fluxing is to avoid occlusionscaused by steel splashing. However, in this case, an energy valence isalso obtained as the oxygen contained in the fluxing gas co-operateswith the flame, thus further improving the efficiency of combustion;

Step 2: Diffuse Flame Burner Mode

Once the burner has been switched on and the scrap has been heated to atemperature of 500-600° C., it is possible to rapidly reach full flamepower in stoichiometric ratio. A slight delay in increasing power shouldbe observed when using a very heavy or closely packed charge (in otherwords very large pieces or ones that have a very high lump density). Itis possible to apply a flame strength 2-4 times those commonly used inconventional applications. The individual flames that constitute theglobal effect of the burner are distributed over a greater area ofscrap, thanks also to the variation in shape caused by the variation inflow-rate as described above, in such a way that the specific thermalflow remains unchanged compared to conventional applications, although afar higher total thermal power is applied. High combustion efficiencyand rapid fuel and supporter of combustion blending cause limitingproperties to flame oxidation. The abatement and melting of the chargein the case in which it is particularly heavy and closely packed can beaided by the variation in the combustion ratio.

Step 3: Hybrid Burner Mode and Modulation of the Stoichiometric Ratio

The temperature of the scrap rapidly increases with the flame and thescrap gradually descends to bath level, thus exponentially reducing theefficiency of the diffuse flame in terms of heat transmission by directradiance and surface convection.

Therefore a progressive changeover is made from the diffuse flame to theconcentrated flame by starting to transfer a part of the oxygenflow-rate from the outer crown of holes to the central nozzle.

Moreover, by increasing the combustion ratio, the progressive increasein free oxygen can allow an even faster scrap melt. However, in thiscase carbon must also be locally injected; the iron oxide producedduring this phase drips downwards and collects in the vat positionedbelow the injector. The speed with which iron oxide is produced in thisphase increases rapidly, thus consequentially requiring the addition ofcarbon and lime in order to protect the refractory from chemical erosionand in order to moderate the iron's oxidizing reaction.

Step 4: Concentrated Flame Burner Mode

Once the charge has been melted by the walls and reaches the level ofthe liquid bath, the changeover to the concentrated flame burner modemust be completed. The subsequent aim is to melt the quantity of scrapthat is found at a distance from the head of the injectors towards thecentre of the furnace. It is very dangerous to hit the scrap with afast, concentrated jet of oxygen as it would create splashes of ironoxide or the jet of oxygen could be reflected backwards towards therefractory panels. It is therefore not possible in this phase to use aninjection of supersonic oxygen to oxygen lance cut the residual scrappresent at bath level. However, this phase does require a long,concentrated flame, but one that does not have an excessive momentum. Inthe concentrated flame burner mode, the injector-burner of the presentinvention satisfies this requirement and has a very directional thermaland chemical action that is able to transfer heat to the charge presentbelow its installation level. By adjusting the stoichiometric ratio, itis also possible to exert an oxidizing action on the residual charge inorder to accelerate the reaching of complete melting.

Whilst the injector is in use in-the concentrated flame mode, the firstdecarburation and oxidising reactions take place. Both the flow ofoxygen flowing out from the central nozzle and the fluxing air or oxygenallow the post-combustion of the CO that has formed. The changeover ofthis step of the procedure is crucial for preparing the last stepefficiently.

Step 5: Refining

The last step is aimed at accelerating all the oxidising reactions ofthe liquid steel bath and the decarburazion reaction in particular. Inthis case the nominal flow-rate is applied from the centralconverging-diverging nozzle. During this phase, the most importantparameter to be monitored is the efficiency of the jet, as it isnecessary to obtain high reaction speed, blending by mass transport, lowoxygen concentrations in the slag and high decarburation inside the bathin order to obtain the best possible operating results.

During the refining phase, the injection of supersonic oxygen can beaccompanied by the injection of methane through the inner crown ofholes, given that the effect of rotation in this latter around theoxygen jet and its combustion with the oxygen injected from the centralnozzle or even from the outer crown of holes promotes the coherency andpenetrating action of the supersonic jet into the bath.

The higher flow-rate methane injection can also be used to obtain acarburation and reduction effect in agreement with the “hybrid oxygeninjection—carburation—reduction and post-combustion mode” describedabove.

In some cases, oxygen injection through the central nozzle can bereplaced for short intervals by the injection of methane through thecentral nozzle, following the “pure carburation mode”. This practicemakes it possible to decarburise the bath and recover metallic yield,thanks to the local reducing effect of the products in which the methanecracks.

FIG. 7 schematically illustrates the series of the injector's operatingmodes throughout the melting process. Oxygen flow-rate #1 is thatinjected by the central converging-diverging nozzle, whereas oxygenflow-rat #2 is that injected by the outer crown of holes. The methaneflow-rate refers to the inner crown of holes.

One can recognise the two diffuse and concentrated flame modes used oneafter the other and separated by a hybrid phase in which anintermediately-shaped flame is created. At the end of the process, asupersonic oxygen injection is performed for bath decarburation. Thisphase can be divided into two separate modes: the first with a methaneinjection around the jet of oxygen (in order to increase jet coherenceand even give a superficial carburation effect to the bath), the secondwith the injection of supersonic oxygen alone.

The profiles given are absolutely general and can be applied as aprinciple for any type of furnace charging (single or multiple buckets)and they refer to an injector using methane and oxygen as fuel andsupporter of combustion respectively.

1. Injector-burner comprising a cylindrical body (3) defining a firstlongitudinal axis (6), the cylindrical body comprising a first centralduct (8) arranged along said first axis (6), at least one secondring-shaped duct (10), arranged around said first central duct (8), athird ring-shaped duct (9), arranged around said second ring-shapedducts (8), a head (2), fixed to one end of said body and provided withat least one first central hole (7), coaxial to the first longitudinalaxis (6) and connecting said first central duct (8) with the outside ofthe cylindrical body (3), the head (2) being provided with second andthird through holes (5) connecting respectively said second and thirdring-shaped ducts (9, 10, 11) with the outside of the injector-burner,the second through holes (5) defining respective second axes, whereineach second respective axis forms a first angle with a plane passingthrough the first axis (6) and an intersection point of said secondrespective axis with an external surface of the head (2) and whereineach second respective axis defines a projection on said plane forming asecond angle with said first axis (6), characterised in that the secondand third through holes are divided into several groups, the groupsbeing reciprocally separated by circular sectors of the external surfaceof the head without holes, whereby the circular sectors have theirapexes on the first axis (6) and their angles are greater than theangular distance between two adjacent second through holes. 2.Injector-burner according to claim 1, wherein each of the said thirdthrough holes define respective third axes forming a first angle with aplane passing through said first axis (6) and the intersection point ofsaid third respective axis with the external surface of the head (2) andhaving a projection on said plane forming a second angle with said firstaxis (6).
 3. Injector-burner according to claim 2, wherein one orseveral of said groups of second and third through holes (5) compriseholes whose axes have first angles with a value different from 0° andsecond angles with a value of 0°.
 4. Injector-burner according to claim3, wherein said several groups of second and third through holes (5) areplaced on the burner head symmetrically and directed in respectivediverging directions with respect to the first axis (6) so that saidseveral groups of second and third through holes (5) are suitable toproduce respective flames in diverging directions and substantiallysymmetrical with respect to said first axis (6).
 5. Injector-burneraccording to claim 2, wherein said first and second angles of therespective axes of second and third through holes have a value comprisedbetween 5 and 60°.
 6. Injector-burner according to claim 5, whereinsecond respective axes and third respective axes, crossover one anotherin pairs outside the injector-burner.
 7. Injector burner according toclaim 6, wherein the second and third holes are distributed on twocircular crowns concentric with the first axis (6) of the cylindricalbody.
 8. Injector-burner according to claim 7, wherein said firstcentral duct (8), or the corresponding first central hole (7), comprisesa portion having a shape of a converging or converging-diverging nozzle(15, 15′).
 9. Injector-burner according to claim 8, wherein an outflowof supersonic gas from the nozzle is provided with a variation in gaspressure along the length of the nozzle (15, 15′) according to ahyperbolic tangent function.
 10. Injector-burner according to claim 9,wherein there is provided a fourth duct (16), inside the first centralducts (8), and substantially coaxial with it, for supplying solid orliquid components, dispersed in a gas.
 11. Injector-burner according toclaim 10, wherein the second and/or third through holes are shaped to aconverging or converging-diverging nozzle.
 12. A method for introducingone or more gases into a melting furnace for metals, wherein said gasesare introduced in the metal through an injector-burner according toclaim
 1. 13. The method according to claim 12, comprising the step ofsupplying an oxygen-containing gas to the first duct of saidinjector-burner and a fuel-containing gas to the second or third duct,so as to generate a flame outside the injector-burner.
 14. The methodaccording to claim 13, comprising the step of ejecting oxygen-containinggas from the first hole of said injector-burner at supersonic velocity.15. The method according to claim 14, comprising the step of making partof said fuel reach unburnt a melt inside the furnace.
 16. The methodaccording to claim 12, comprising the step of supplying anoxygen-containing gas to the third duct of said injector-burner.
 17. Themethod according to claim 12, comprising the step of supplying afuel-containing gas to the third duct and an oxygen-containing gas to asecond duct.
 18. The method according to claim 12, comprising the stepof supplying an oxygen-containing gas from the first duct of theinjector-burner.
 19. The method according to claim 18, comprising thestep of ejecting gas from the first hole of the injector-burner atsupersonic velocity.
 20. The method according to claim 19, comprisingthe step of producing a coherent length of a gas jet from said firsthole greater than the distance of the head of the injector-burner fromthe surface of a melt contained in the furnace.
 21. The method accordingto claim 12, comprising the step of introducing a solid in form ofpowder or granules through the injector-burner first duct.
 22. Themethod according to claim 21, comprising the step of introducing thesolid together with a gas stream, whose outflow from the first hole ofthe injector-burner is subsonic.
 23. The method according to claim 12,comprising the step of introducing a solid in the form of powder orgranules through the fourth duct.
 24. The method according to claim 12,comprising the step of supplying a fuel-containing gas to the first ductof said injector-burner in subsonic or supersonic regime.
 25. The methodaccording to claim 24, comprising the step of making-part of said fuelreach unburnt the surface of a melt inside the furnace. 26.Injector-burner according to claim 4, wherein the second and third holesare distributed on two circular crowns concentric with the first axis(6) of the cylindrical body.
 27. Injector-burner according to claim 26,wherein said first central duct (8), or the corresponding first centralhole (7), comprises a portion having a shape of a converging orconverging-diverging nozzle (15, 15′).
 28. Injector-burner according toclaim 27, wherein an outflow of supersonic gas from the nozzle isprovided with a variation in gas pressure along the length of the nozzle(15, 15′) according to a hyperbolic tangent function. 29.Injector-burner according to claim 28, wherein there is provided afourth duct (16), inside the first central duct (8), and substantiallycoaxial with it, for supplying solid or liquid components, dispersed ina gas.
 30. Injector-burner according to claim 29, wherein the secondand/or third through holes are shaped to a converging orconverging-diverging nozzle.
 31. Injector-burner according to claim 30,wherein said injector-burner is mounted on a lance fitted with amechanical arm.
 32. Injector-burner according to claim 11, wherein saidinjector-burner is mounted on a lance fitted with a mechanical arm. 33.The method according to claim 14, comprising the step of supplying afuel-containing gas to the second duct of the injector-burner.
 34. Themethod according to claim 16, comprising the step of supplying afuel-containing gas to the first duct of said injector-burner insubsonic or supersonic regime.
 35. The method according to claim 34,comprising the step of making part of said fuel reach unburnt thesurface of a melt inside the furnace.